A presensitized planographic printing plate is well known which comprises a positive working light sensitive composition capable of being solubilized by actinic light irradiation.
As a light sensitive material comprising a positive working light sensitive composition to be solubilized by actinic light irradiation, an image forming material comprising a light sensitive layer containing an acid generating compound and an acid decomposable compound is known. For example, a light sensitive composition containing an orthocarbonic acid, or a compound having a carbonic acid amide acetal group is disclosed in U.S. Pat. No. 3,779,779, a light sensitive composition containing a compound having an acetal in the main chain is disclosed in Japanese Patent O.P.I. Publication No. 53-133429, and a light sensitive composition containing a compound having a silylether group is disclosed in Japanese Patent O.P.I. Publication Nos. 60-37549 and 60-121446. These compositions have sensitivity in the ultraviolet range. In image forming materials comprising a light sensitive layer containing these compositions, the light sensitive layer is alkali solubilized by imagewise ultraviolet ray exposure to provide non-image portions at exposed portions and image portions at non-exposed portions.
In Japanese Patent Publication Nos. 52-7364 and 52-3216 is disclosed a negative working light sensitive material in which when the material is exposed to actinic light, photo-polymerization or photo-crosslinking reaction occurs at exposed portions to form an image. Ultraviolet rays are used for an exposure source as in the positive working light sensitive material. In U.S. Pat. No. 5,340,699 is disclosed an image forming material comprising a light sensitive layer containing an acid generating compound, an acid crosslinking materal (a resol resin), a binder (a novolak resin) and an infrared absorber, wherein the material is exposed to infrared rays, and the exposed portions are insolubilized in an alkali.
Recently, improvements in processability have been required. In printing industries, a plate-making process comprising easily editing through software, so-called CTP (computer to plate process), has appeared before the footlights as an alternative of conventional editing processes requiring many hands. CTP is a process capable of recording digitally employing an inexpensive and compact infrared laser. This technique employs an image forming material comprising an infrared absorbent as an essential component which is capable of absorbing an infrared laser. The image forming material enables an image forming method comprising imagewise exposing to infrared semiconductor laser to form an image.
Ordinarily, these image forming materials are imagewise exposed, and then developed with a developer which is recirculated and is replenished with a developer replenisher. During development, components in the light sensitive layer, particularly acid decomposed components, are incorporated into the developer. In this process, however, there are problems in that the incorporation results in fluctuation of developability of the developer and in sludge occurrence (precipitates and/or floating matter) due to insufficient solubility of the components. Particularly, the sludge adheres to the image forming materials to be developed, resulting in stains. When the process described above is applied to manufacture of a printing plate, such stains produce a large number of paper wastes during printing, which incurs a great loss.
The above problems become more noticeable as the amount of image forming materials to be processed increases and the replenishing amount of the developer replenisher is reduced. Particularly when a developer containing a silicate is used as a developer, the problems are most prominent, and resolution thereof is required for practical use.
CTP has a problem in that satisfactory sensitivity is not obtained as compared to conventional UV ray exposure. Further, the above described light sensitive materials have poor storage stability and poor safelight safety property. For example, in the conventional positive working light sensitive material, sensitivity and dot reproduction are fluctuated, and in the conventional negative working light sensitive material, stain is likely to occur. With regards to safelight safety property, white light resistance is not sufficient. In the positive working light sensitive material, the thickness of the radiation sensitive layer is decreased on development under white light lamp, resulting in lowering of printing durability, and in the negative working light sensitive material, stain is likely to occur at non-image portions. Resolution of the above problems is required.